1. Field of Invention
This invention relates to silicone elastomeric foams produced by mixing two parts together, said mixture frothing and curing at room temperature.
2. Background Information
A number of methods have been developed over the years for producing foam based upon elastomeric silicone polymers. A composition was disclosed by Modic in U.S. Pat. No. 3,425,967, issued Feb. 14, 1969, that gave improved strength and flame retardancy in the foamed state by including inorganic fibrous material in a composition which produced a foam because it contained a blowing agent which released an inert gas when the composition was heated. Smith disclosed a method of making elastomeric silicone foam at room temperature in which the foam was formed upon mixing of the ingredients. The foam formed was stated to be fire retardant and non-toxic. His method, disclosed in U.S. Pat. No. 3,923,705, issued Dec. 2, 1975, mixes an organohydrogensiloxane, a hydroxylated organosiloxane, and a platinum catalyst. The reaction simultaneously generates hydrogen to form the foam and crosslinks the polymer to cure the foam. He discusses varying the density of the foam by changing the ratio of silicon-bonded hydrogen to silicon-bonded hydroxyl as well as the filler loading. Such changes would also change the crosslink density of the cured foam.
A composition which formed a foam, upon heating above 125.degree. C., that had a thin skin or no skin was disclosed by Kittle in U.S. Pat No. 4,026,843, issued May 31, 1977. His composition was based upon a gum base stock to which an organic alcohol having one C-OH per molecule, optionally hydroxyl-endblocked polydiorganosiloxane fluid, organohydrogensiloxane, acetylenic alcohol inhibitors, and platinum catalyst are added.
A method of decreasing the density of a silicone foam comprising a hydroxylated organosiloxane, an organohydrogensiloxane, and a platinum catalyst was disclosed by Kim et al. in U.S. Pat. No. 4,026,845. They obtain lower density by adding a fluorinated surfactant to the composition. They define such materials to be those compounds known in the art which contain fluorine atoms on carbon and are also surfactants. Examples are perfluorinated polyethers and siloxanes containing organic radicals having fluorine bonded thereto.
Another method of reducing the density of a silicone foam is disclosed by Modic in U.S. Pat. No. 4,418,157, issued Nov. 29, 1983, by adding a resinous copolymer to a foamable silicone composition having a base polydiorganosiloxane, an organohydrogensiloxane, and a platinum catalyst. The resinous copolymer consists of resinous copolymers of R.sub.3 SiO.sub.1/2 units and SiO.sub.2 units; and resinous copolymer of R.sub.3 SiO.sub.1/2 units, R.sub.2 'SiO units, and SiO.sub.2 units.
U.S. Pat. No. 4,518,726, issued May 21, 1985, to Lee and Rabe describes the use of resinous benzene-soluble organosiloxanes having fluorine-containing units as foam stabilizers for use in moisture-curing silicone elastomeric foams which are stored in the absence of moisture in aerosol containers. The foam is formed by releasing the contents to the atmosphere, the foam forming upon release of the pressure and then curing by reacting with the moisture in the air.
The above references disclose methods of making elastomeric silicone foams and means for lowering the density of the foam. The references do not teach how to obtain more uniform foam with finer cells. The references do not teach how to obtain different combinations of foam properties such as density, compressibility and resiliency.
Accordingly, means for controlling foam properties such as compressibility and resiliency as well as density were desirable for use with different foamable silicone compositions. Means for producing silicone foams having a density of less than 160 kg/m.sup.3 and a compressibility at 25 percent compression of less than 24 kPa while retaining useful strength were desired.